The physical and chemical structure of Sagittarius B2 -- V. Non-thermal emission in the envelope of Sgr B2

F. Meng; Á. Sánchez-Monge; P. Schilke; M. Padovani; A. Marcowith; A. Ginsburg; A. Schmiedeke; A. Schwörer; C. DePree; V. S. Veena; Th. Möller

doi:10.1051/0004-6361/201935920

arXiv · 1908.07237

The physical and chemical structure of Sagittarius B2 -- V. Non-thermal emission in the envelope of Sgr B2

F. Meng·Á. Sánchez-Monge·P. Schilke·M. Padovani·A. Marcowith·A. Ginsburg·A. Schmiedeke·A. Schwörer·C. DePree·V. S. Veena·Th. Möller

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Abstract

The giant molecular cloud Sagittarius B2 (hereafter SgrB2) is the most massive region with ongoing high-mass star formation in the Galaxy. In the southern region of the 40-pc large envelope of SgrB2, we encounter the SgrB2(DS) region which hosts more than 60 high-mass protostellar cores distributed in an arc shape around an extended HII region. We use the Very Large Array in its CnB and D configurations, and in the frequency bands C (4--8 GHz) and X (8--12 GHz) to observe the whole SgrB2 complex. Continuum and radio recombination line maps are obtained. We detect radio continuum emission in SgrB2(DS) in a bubble-shaped structure. From 4 to 12 GHz, we derive a spectral index between -1.2 and -0.4, indicating the presence of non-thermal emission. We decompose the contribution from thermal and non-thermal emission, and find that the thermal component is clumpy and more concentrated, while the non-thermal component is more extended and diffuse. The radio recombination lines in the region are found to be not in local thermodynamic equilibrium (LTE) but stimulated by the non-thermal emission. The thermal free-free emission is likely tracing an HII region ionized by an O7 star, while the non-thermal emission can be generated by relativistic electrons created through first-order Fermi acceleration. We have developed a simple model of the SgrB2(DS) region and found that first-order Fermi acceleration can reproduce the observed flux density and spectral index.

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F. Meng, Á. Sánchez-Monge, P. Schilke, M. Padovani, A. Marcowith, A. Ginsburg, A. Schmiedeke, A. Schwörer, C. DePree, V. S. Veena, Th. Möller. 2019-08-20. The physical and chemical structure of Sagittarius B2 -- V. Non-thermal emission in the envelope of Sgr B2. https://doi.org/10.1051/0004-6361/201935920

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